Compressed air circuit breaker



Nov. 20, 1951 FORWALD 2,575,949

COMPRESSED AIR CIRCUIT BREAKERS Filed Feb. 17, 1948 gr a 1 INVENTOR I ,e m/m/r FORM/4!. 0

ATTORNEY Patented Nov. 20, 1951 COIVIPRESSED AIR CIRCUIT BREAKER Haakon Forwald, Valhalla, Ludvika, Sweden, assignor to Allmiinna Svenska Elektriska, Aktiebolaget, Vasteras, Sweden, a Swedish corporation Application February 17, 1948, Serial No. 8,894 In Sweden July 17, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires July 17, 1963 1 Claim. 1

In electric circuit breakers, in which the extinction of the breaking arc is performed by means of compressed air, it is of great importance that all steps to save air are taken, because thereby the air accumulator can be given smaller dimensions and the circuit breaker therefore be made cheaper. In some of the hitherto known circuit breakers attempts have been made to save compressed air by closing the air delivery to the circuit breaker immediately after the extinction of the breaking arc. Such an arrangement is, however, combined with the disadvantage that the arc can be reignited after the extinction due to the fact that the insulating strength of the air at atmosphere pressure is considerably lower than the pressure during extinction. In order to avoid this disadvantage, it has been proposed to close the outlet from the circuit breaker after the extinction, so that the breaking gap will remain under the same pressure as that prevailing during the extinction of the arc. The closing of the outlet from the circuit breaker is, however, a step followed by the disadvantage that the closing members are destroyed by the hot gases escaping from the circuit breaker.

The present invention has for its object an arrangement, by which a considerable saving of compressed air is reached by very simple and reliable means. The invention is based upon the observation that for a given distance between the contacts a substantially lower pressure is necessary for the insulation after extinction than the pressure necessary for the extinction. According to the invention, the circuit breaker is provided with arrangements, which immediately after the extinction of the arc reduce the pressure in the circuit breaker to a value considerably lower than the pressure prevailing at the extinction, said arrangements maintaining this value either until a disconnecting switch connected in series with the circuit breaker has been opened or until the contacts have been separated so far that no arc can be ignited again at atmospheric pressure. Such an arrangement can for instance consist of a valve in the delivery line for the compressed air, which valve immediately after the extinction of the arc restricts the delivery of the air, so that the pressure is reduced in the above said manner.

One form of the invention is illustrated on the accompanying drawing, on which 6' and l designate contacts forming an arcing gap, and on which and 1 designate an arcing chamber connected with an insulating cylinder 4 by means of a connecting-piece 5, such cylinder 4 being carried by a compressed air container I resting upon a stand 2. An air blast valve I4 is provided with an operating piston 15, movable in a cylinder l2, compressed air being delivered to said cylinder I 2, from the container l, by the opening of an electrically actuated pilot valve [6. In series with the air blast valve i4 is a throttle valve I! which is shown on the drawing in its partly closed or throttling position. This valve I1 is normally held open by a helical spring l8 acting on a piston l9, movable in a cylinder l 3, and the valve I1 is moved to throttling position by compressed air passing from the valve [4 by way of a pipe line 29 and a needle valve 2|, said air acting on the piston 19 to move the valve I! to its partly closed position shown. By adjustment of the needle valve 2!, the downward motion of the piston l9 can be regulated to delay the closing motion of the throttle valve I! to the desired value. The downward motion of the piston l9 and Valve I! is limited by a collar 22 surrounding the rod 23 connecting the valve I! with the piston 19, so that, when the piston I 9 has reached its lowermost position, there is still a valve opening permitting compressed air to reach the arcing chamber 6, 1 in order to maintain a reduced pressure in said chamber sufficient to prevent reignition of the arc. In the meantime, the switch arm 8 of the disconnectin switch is, by means of an operating rod H, raised out of contact with the contact 9, which is carried by the insulator I0.

I claim as my invention:

In an air blast circuit breaker having an arcing gap, a disconnecting switch in series with the arcing gap, a compressed air container, a main valve controlling the supply of extinguishing air from the container to the arcing gap, and a throttle valve interposed between said main valve and the arcing gap, said throttle valve being normally open and commencing to close when exposed to the pressure from said container, and said closing being so delayed that extinction of the arc takes place before the throttle valve reaches its final throttling position with an opening suflicient to maintain an air pressure that prevents re-ignition of the arc.

HAAKON FORWALD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,937,482 Ruppel Nov. 28, 1933 2,125,525 Thommen Aug. 2, 1938 2,306,186 Rankin Dec. 22, 1942 2,331,441 Thommen et a1 Oct. 12, 1943 

